It's the 50th year of Doctor Who and look what's going on! We're up in the sky and under the sea! We're running round the rings of an alien world and then a haunted house. There's new Cybermen, new Ice Warriors and a never before attempted journey to the centre of the TARDIS. And in the finale, the Doctor's greatest secret will at last be revealed! If this wasn't already our most exciting year it would be anyway!

The episode itself is described as:

Set in London against the backdrop of new and old iconic landmarks, The Shard and Westminster Bridge, 'The Bells of St John' will also establish a new nemesis, the Spoonheads, who will battle the Doctor as he discovers something sinister is lurking in the Wi-Fi.

To tie in with the series return, they have also released a promotional image featuring the Doctor and Clara 'crashing' through the Shard in London:

Both the portrait and landscape versions offer tantalising glimpses of some of the enemies the couple will face in the coming eight weeks ... including the new-look Ice Warriors which have been confirmed as appearing in the third episode. Writer Mark Gatiss said:

I've always loved the iconic Ice Warriors and have been badgering to bring them back for ages. And now they're on a ssssssubmarine! With Russians! I'm a very happy anorak right now.

The episode features guest star David Warner, and resident voice actor Nicholas Briggs has confirmed that he will be bringing the Doctor's old adversary to life.